Structure And Dynamics Of Colloidal Systems Under Random Pinning

The structure and dynamics of the matter are the eternal research topics in condensed matter physics.Under certain conditions,colloidal system which can form liquid,crystal or glass,is a commonly used exper:imental model in condensed matter physics,playing a crucial role in the study of crystallization,melting and glass transition.In colloidal system,confinement is one of the most important ways to control the condensed state behavior of colloidal system.There are various kinds of restrictions,random pinning is one of the focuses of research in recent years.Currently,random pinning is mostly used on theoretical studies and computational simulation studies.For example,computational simulation had shown that when the random pinning is used to control system behaves,it can slow down the dynamics,and increasing the concentration of pinning particles can transform the system from liquid to glass.However,the experiments on random pinning have rarely been reported.In this paper,we study the structure and dynamics of colloidal system by adding random pinning particles to the system.The optical camera microscopy was used to observe and photograph the samples,and the captured images were analyzed by using particle tracking technology to obtain the structural and dynamic information of the colloidal system.The main contents and results are as follows:1.Effect of random pinning on colloidal structure and dynamics.By confining the colloidal hard sphere particles to two glass slides,and then heating and drying,we successfully get a pinning system with random distribution and adjustable concentration.The sedimentation method is used to study the structure and dynamics of the colloidal system under random pinning.We find that when the area fraction of the system is sufficiently high and close to the glass transition point,the dynamic behavior of the system becomes slower with the increasement of the pinning particles,and in the samples with the same pinning,the similarity of configurations of the two systems will increase with the increasement of the pinning particles.2.Random pinning induces a two-dimensional crystal to glass.We experimentally investigate the effect of pinning on the structure and dynamics of crystal-to-glass translation in the quasi-two-dimensional binary colloidal suspensions.The system forms a perfect crystal without pinning particles.But when increasing the pinning particles,the system gradually shifts from a crystal to a glass.With the increasement of pinning particles,the system gradually changes from order to disorder.And when the concentration of the pinning particles reaches 14%,the dynamics changes greatly and the dynamic heterogeneity grows rapidly.